The RNF43 gene (17q22) encodes the RNF43–Ring Finger Protein 43 (783 amino acids; 85,722 Da), which probably negatively regulates the WNT signaling pathway, its defects being identified in sessile serrated polyposis cancer syndrome and colorectal cancer, as well as in multiple tumor types, including colorectal and endometrial cancers [222]. This evidence concerns the gene RNF43 and sessile serrated polyposis cancer syndrome.